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Altera_Forum
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14 years ago

problem with LCD Refreshing rate

Hello,

I recently designed a model in Quartus which connects to a color LCD device and shows what ever is on the SRAM.

I am using the NIOS processor to fill the RAM with the relevent Data (PICS,ANIMATIONS and so).

One problem is that the reading cycle time of a byte is 55nsec.

the LCD can work up to 33MHZ(840X480) so I'm not able to fully use the LCD's Resolution(I'm using 8 MHZ which is 480X272 Res).

another Problem is the Data size (24 bits - 8 red + 8 green + 8 blue).

I cant write 2 cycles on the sram for every Pixel because it doesent match the 8 MHZ timing.

so what i did is to normalize the data bits to 15 bits per each pixel (5r+5g+5b) and decrase the lcd's speed to 8 mhz

for every screen I want to load I need to fill up the ram with 480*272 Addreses(130.5Kbytes).

The problem is that the NIOS clk seem to be 50MHZ but the actual one is much slower,so it takes me about 2 secs to fill up the sram.

that gives me a slow refresh rate on the LCD.

are there any sugesstions to make the NIOS RUN faster?

Is my techniqe OK?

are there any other good methods to work with LCD so I would able to exploit the SPEED and pixel bits?

thanks for all the helpers,

Asaf

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  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Hi

    i tried to use the cross bridge

    now the add and dat lines doesnt work well .

    It seems like the dat line became 8 bit instead of 16

    and also,timing still very slow comparing to the clock on the cpu

    any suggestions?
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    I remain on my original advice: use the standard sram interface module provided by sopc builder. Then you can easily tune all the parameters, access timing, waitstates, data and address width.

    For extra performance you can connect the sram to a Nios TC port, instead of the main data master. This will avoid stalls due to arbitration with other MM devices.

    Anyway, I don't see a reason to optimize further; I think you can attain a good refreshing rate without effort.
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Ok then...

    I just need to know what is the way to read and write data from the nios to the sram

    thank u very much
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    I can't understand your concern with sram. You access sram like any other kind of memory.

    e.g. you can use sram base address with IOWR/IORD for direct access;

    alternatively you can map C variables/buffers (or even an entire memory section) to sram physical addresses.

    Example:

    int * lcd_buffer = (int*)LCD_SRAM_BASE;

    for (i=0; i<num_of_pixels; i++) {

    lcd_buffer[i] = <your graphic data>;

    }
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    As Cris72 said - you can also do that into your own Avalon slave.

    You do need to write one - it isn't hard, and the 'PIO' slave won't really give you the flexibility you need.

    You also need ensure your slave defines all 32 data bits - even if you ignore the high ones.

    If you set a C pointer to IO, remember to set bit31 so that the data cache (if used) is bypassed.

    One 'cheat' method I've sometimes used to determine which parts of a system are taking the time, is to do some parts twice. If it makes no difference it isn;t the problem!
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    thanks...

    I understand how to write data to the ram...the tricky part with your suggestion is to read the ram without using the nios.

    Thats what i have left to do...how can i write from the nios and read from the mode?

    I dont want to spend time on presenting the picure from the cpu..just want to set the data from the cpu and read it from out side the processor...any suggestions?
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    I can't get the point. Probably I still don't understand what you want to do.

    Please clarify.

    - where your picture data is stored?

    - how are you supposed to get this picture data?

    - do you want to use Nios for the transfer or not?

    - is LCD actually seen as a sram or a more complex interface is required? I mean, if you write a sram address, the related pixel changes on the display? Or maybe a special protocol is involved for transferring the display image?
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    --- Quote Start ---

    I can't get the point. Probably I still don't understand what you want to do.

    Please clarify.

    - where your picture data is stored? on the sram addresses

    - how are you supposed to get this picture data?from an external vhdl model which reads from the sram and sends the pic according to the svreen protocol

    - do you want to use Nios for the transfer or not?only for the writing

    - is LCD actually seen as a sram or a more complex interface is required? I mean, if you write a sram address, the related pixel changes on the display? Or maybe a special protocol is involved for transferring the display image?special serial protocol...you can look at terasic's touch screen

    --- Quote End ---

    http://www.terasic.com.tw/cgi-bin/page/archive.pl?language=english&no=213
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Q: Is there display memory on the display module? or do you have to continuously clock the pixel data to it (from the dev board SRAM)?